The invention relates to a band saw and more particularly to a tubular band saw.
It is well known in the prior art to form a band saw blade from a thin, flat, flexible ribbon with teeth mounted thereon. One of the great disadvantages of such band saws are that they are relatively directional, that is, the direction of cut cannot be changed easily simply by rotating the saw or the workpiece. Furthermore, even in band saws having a relatively narrow saw blade either the workpiece or the entire saw must be rotated in order to change the direction of cut.
In order to overcome this disadvantage, tubular band saws were developed, such as described in U.S. Pat. Nos. 152,970 and 2,043,603. In the device described in U.S. Pat. No. 152,970 a continuous tubular saw blade is described whereas in U.S. Pat. No. 2,043,603 a cable with a plurality of tubular cutting links thereon is described. In both prior art devices the cutting elements are driven by a pulley over which the saw blade travels. Moreover, in the device described in the latter patent the pulley moves the cable by pushing the cutting elements through the cut made in the material.
There are several disadvantages to such prior art tubular band saws. One disadvantage is that there is a tendency for sawdust and chips to cling to the cutting elements and thus to clog the saw blade. This problem is compounded by the fact that the saw blade passes over a pulley which further tends to compact the loose waste material into the cutting edges of the blade. Still another disadvantage of the band saw described in U.S. Pat. No. 2,043,603 is that because the pulley tends to push the saw blade through the workpiece there tends to be a flaring of the hole on the entry side of the cut in the workpiece. There is also the tendency of such saws to become unduly twisted because the lay of the cutting teeth is substantially continuous and in the same direction along the length of the blade. Still another disadvantage of the pulley drive system is that the saw blade is likely to slip and to wear out the pulley whenever the saw blade encounters a portion of the workpiece which is more difficult to cut.